The present invention relates to a two-phase charge-coupled device with a single-layered electrode structure where a pair of potential barrier region and a charge storage region are disposed underneath one charge transfer electrode, and more particularly to a method for producing the charge-coupled device.
There are two types of charge-coupled devices: a 2-phase, 2-ply-electrode-type charge-coupled device and a 2-phase, single-ply electrode-type charge-coupled device.
The 2-phase, 2-ply electrode type charge-coupled device is disclosed in references: JP-A-192561/1992, JP-4133/1986, and IEDM Technical Digest, 1974, pp 55-58. This charge-coupled device is fabricated as follows:
Referring to FIGS. 12(A) to 12(E), an N-type semiconductor region 702 is first formed on a P-type semiconductor substrate 701. Then, a first insulating film 703 is formed on the surface of the N-type semiconductor region 702 though a heating process (FIG. 12(A)).
A first conductive electrode 704 of polycrystalline silicon is formed on the first insulating film 703 (FIG. 12(B)). As seen in FIG. 13, the first conductive electrode 704 has a rectangular top pattern. FIG. 13 is a schematic plan view corresponding to FIG. 12(B). The first conductive electrodes 704 are disposed at constant intervals.
Next, impurities (e.g. boron) of a conductivity type opposite to that of the N-type semiconductor region 702 are implanted into regions between the first conductive electrodes 704, so that a N.sup.- -type semiconductor region 705 is formed (FIG. 12(C)). FIG. 14 is a schematic plan view corresponding to FIG. 12(C).
In succession, the first insulating film 703 is removed with the first conductive electrode 704 acting as a mask. Thereafter, the intermediate structure is again subjected to a heating process to form the second insulating film 706. A second conductive electrode 707 of polycrystalline silicon is formed on the second insulating film 706 corresponding to the first conductive electrode 704 and the N.sup.- -type semiconductor region 705 (FIG. 12(D)). FIG. 15 is a schematic plan view corresponding to FIG. 12(D).
Next, an interlayered insulating film 708 is disposed. Electrodes are interconnected with metal conductors 709 (FIG. 12(E)). Thus, a conventional 2-phase, 2-ply electrode charge-coupled device is fabricated.
The progress of the micro patterning technique has allowed a single-ply electrode-type charge-coupled device with a electrode spacing of 0.2 to 0.3 .mu.m to be fabricated by etching single-ply conductive electrode materials.
The charge-coupled device with the single-ply electrode structure has no electrode portions overlapped. This structure provides a small capacitance between layers and raises no insulation fault between electrodes. Moreover, the oxidizing process is not required to form the interlayered film. This allows metal films or silicide films to be used as an electrode material, instead of the polycrystalline silicon, so that the resistance component of the electrode can be decreased.
The 2-phase, single-ply electrode type charge-coupled device is fabricated according to the FIGS. 16(A) to 16(D).
An N-type semiconductor region 802 is first formed on a P-type semiconductor substrate 801. Then, the intermediate structure is subjected in a heating process to form an insulating film 803 on the surface of the N-type semiconductor region 802 (FIG. 16(A)).
Next, impurities (e.g. boron) of an opposite conductivity type to the second conductivity type of the N-type semiconductor region 802 are implanted with a photoresist in a predetermined pattern acting as a mask. Thus, the N.sup.- -type semiconductor region 805 is formed (FIG. 16(B)). FIG. 17 is a schematic plan diagram corresponding to FIG. 16(B).
In succession, a conductive electrode 804 of a polycrystalline silicon is formed on the insulating film 803 (FIG. 16(C)). The conductive electrode 804 is patterned so as to have a pair of a charge storage region and a potential barrier region. FIG. 16(C) is a schematic plan diagram corresponding to FIG. 16(C).
Next, an interlayered film 808 is formed on the surface of the intermediate structure. Electrodes are interconnected with metal conductors 809 (FIG. 16(D)).
Thus, a conventional 2-phase drive type charge-coupled device with a single-ply electrode structure can be obtained.
On the other hand, in the 2-phase, 2-ply electrode type charge-coupled device, the potential barrier region is self-aligned with the charge transfer electrode and is formed in a rectangular pattern. In this structure, it has been difficult to provide a potential distribution sloped in the charge transfer direction to facilitate the charge transfer.
JP-A-192561/1994 discloses a solid-state image pickup device having slanted electrode patterns. However, even in this image pickup device, since the potential in the charge storage region becomes shallow gradually in a charge transfer direction, the advantages of the present invention cannot be obtained.
Moreover, the same problem arises in the above-mentioned single-ply electrode, 2-phase drive charge transfer device.